I’m not sure how you troubleshoot noise in a stereo system with the loudspeakers disconnected, but otherwise, while this isn’t the way I’d track down noise, the general idea is ok.
First is to determine if the noise is common to both channels and if the noise is present with all the sources connected to the system, go from there.
When problems arise in our stereo systems we’re often at wit’s end to resolve them. I cannot tell you the number of exasperated calls and emails I have received from customers who have “tried everything” without success.
Of course, trying everything is akin to having looked everywhere for something lost. Neither statement can be true. Clearly, one hasn’t looked where the missing item is, nor can it be said you’ve tried everything since you haven’t tried the one thing that will fix the problem.
When trouble occurs, it’s best to take a deep breath, wash away all your assumptions, and begin to narrow your focus to specific elements within the chain. This is the tried and true way of troubleshooting known as the Process of Elimination. We selectively eliminate pieces of the electronic chain until the errant device is identified.
Narrowing down the problem to one section, one piece, or one process is the key to effective troubleshooting. My preference is to start at the output and work backward. So, for example, if there’s an annoying noise coming from your speakers, disconnect the cables feeding your speakers and see if the noise stops. It probably will. Next, connect the next piece in the chain, typically the amp and its cables—but make sure the amp hasn’t anything connected to its inputs. Noise? It’s the amp. No noise? Keep working down the chain.
By narrowing your focus you hone in on the bad citizen. From there, you repeat the process of elimination process on the device itself until finally you understand what went wrong.
Always a great skill to keep in one’s back pocket.